Thus far, I think there's only been one synth manufacturer that's released a stompbox case, the Pittsburgh Modular Patch Box. And there is one specific, overriding reason for this:
Do you really want delicate module controls in the same enclosure that you're supposed to be poking at with your shoes? A single misstep can be awfully expensive.
Don't do this. Put the controls on the floor, sure...but NOT the modules!!!